Probably not especially difficult to port the platform-specific bits from OpenBSD to NetBSD, but also not trivial.

A lot of the "wow, this actually Just Works on OpenBSD!" support is because one or more OpenBSD developer actually runs the given system. Supposedly that's why there's really good support for a large number of laptop peculiarities that NetBSD lacks -- OpenBSD devs are actually dailying OpenBSD on those machines.